In general, an accumulating conveyor has a plurality of zones which can be selectively controlled to allow the articles being conveyed to accumulate in a selected area of the conveyor. Accumulation of articles is accomplished by disengaging the drive means from the conveyor rollers in the "accumulation zone", while zones upstream continue to convey articles downstream. When the initial accumulation zone is filled, the next adjacent upstream zone is halted so that articles will accumulate in that zone. As each successive zone fills, the status of the next adjacent upstream zone is changed to an accumulation mode. In this manner, articles can be backed-up from the discharge end of the conveyor to the infeed end. When the first article in the accumulation mode zone is removed, each zone is activated in sequence to advance the articles downstream.
As articles butt against one another in the accumulation zone, there is a possibility of some articles being jarred, smashed or otherwise damaged by the impact between loads. To avoid this problem, some accumulation conveyors sense the presence of an article in one zone and deactuate or disengage the drive for the next adjacent upstream zone. By selectively controlling each zone in this manner, the conveyed articles remain spaced apart and do not contact during accumulation.
While zero-pressure accumulating conveyors avoid damage to the articles being conveyed, there are some applications where it is desirable to "close-pack" the articles. That is, in some applications it is desirable to butt the articles being conveyed against one another in the accumulation zone. Therefore, there is a need for an accumulating conveyor which can close-pack articles without damage to the articles.
Another problem with prior art accumulating conveyors is that they require complicated mechanisms for alternatively engaging and disengaging the drive means and for braking the rollers. Such mechanical devices take up a large amount of space, are noisy during operation, and require maintenance.
Similarly, most prior art accumulating conveyors also require one or more photoelectric switching devices or weight sensing devices for proper operation. The placement of these photoelectric switches or other sensing devices is critical, and these types of sensing devices are subject to false indications as a result of improper placement.